In an LTE communication system, in order for a user device to transmit and receive data over the air interface, the user device needs to be allocated physical radio resources, and the user device must be notified of its resource assignments by means of control signalling. In LTE, the physical downlink control channel (PDCCH) carries scheduling assignments and other control information, and the PDCCH resources used to signal scheduling assignments to users in the cell are dynamically allocated by the serving base station.
A PDCCH consists of an aggregation of one or more consecutive control channel elements (CCEs), where a CCE occupies a fraction of the base station cell's available physical radio resources. The total number of CCEs available in a cell depends on the system bandwidth of the cell and the number of OFDM symbols reserved for PDCCH transmission in a given sub-frame. Typically, the first three symbols of a sub-frame are reserved for the PDCCH. With LTE Release 11 and beyond additional control channel information can be included using radio resources usually assigned for the Physical Downlink Shared Channel (PDSCH). One example of such additional control channel information is called the enhanced PDCCH (ePDCCH). However, the provision of an ePDCCH in the PDSCH causes problems for the efficient allocation of resources within the PDSCH (as it results in the fragmentation of resources that are allocated) and additional resource allocation techniques are required to address these inefficiencies.